Method of Improving the Biocidal Efficacy of Dry Ice

ABSTRACT

A manufactured dry ice product containing ozone entrapped or absorbed on said dry ice. The dry ice product can be used to chill and preserve food products and provides the added benefit of ozonation of the food product to kill bacteria. Novel processes for ozonating liquid and solid CO 2  are provided.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. Non-Provisionalapplication Ser. No. 11/621,857, filed Jan. 10, 2007, which is acontinuation of U.S. Non-Provisional application Ser. No. 10/632,232,filed Jul. 31, 2003, now U.S. Pat. No. 7,174,744, which claimed priorityto U.S. Provisional application 60/404,635, filed Aug. 20, 2002, andU.S. Provisional application 60/459,398, filed Apr. 1, 2003. Each of theforegoing disclosures are incorporated herein by reference in theirentireties.

FIELD OF THE INVENTION

The present invention is directed to a novel dry ice composition usefulin the preservation of food and other perishable products. The inventionis also directed to novel methods of making the dry ice composition. Thecomposition of this invention and use thereof significantly improves thequality of food products and enhances food safety.

BACKGROUND OF THE INVENTION

The protection of food from damage caused by microbes, spores, insects,and other similar sources is a major concern. Each year, economic lossesof food and fiber due to damage from such sources is more than $100billion. Currently, food items are preserved using a variety of methods,including refrigeration, fumigation with toxic chemicals, irradiation,biological control, heat exposure, and controlled atmosphere storage (afruit industry technique that involves modifying the concentration ofgases naturally present in the air).

The primary problem regarding food spoilage in public health ismicrobial growth. If pathogenic microorganisms are present, then growthcan potentially lead to food-borne outbreaks and significant economiclosses. Food safety concerns have been brought to the consumers'attention since the early part of the 20^(th) century and those concernshave become even stronger today. Recent outbreaks from Salmonella and E.coli have increased the focus on food safety, including from aregulatory perspective. A report issued from National Research Council(NRC) in 1988 indicated that there were approximately 9,000 human deathsa year from 81 million annual cases of food poisoning. A recent studycompleted by the Centers for Disease Control and Prevention (CDC)estimated that food-borne diseases cause approximately 76 millionillnesses, 325,000 hospitalizations and 5,000 deaths annually in the US.Those numbers reveal the dramatic need for effective means of handlingfood products in order to ensure food safety.

As discussed briefly above, food manufacturers use differenttechnologies to eliminate, retard, or prevent microbial growth, such asheating. Even though heat is very efficient in killing bacteria, it alsodestroys some nutrients, flavors, or textural attributes of foodproducts.

Effective sanitation depends on the combination of product andsanitation process type, and not all of the currently availabletechnologies can deliver an effective reduction of microorganisms and atthe same time prevent product or environmental degradation.Refrigeration is an effective and popular means to slow down the growthof unwanted microbes and enzymatic reactions in foods. Therefore, theshelf life and keeping quality of refrigerated food is extended. Somecommon ways of chilling food include the use of mechanical refrigerationequipment, ice, and dry ice.

Dry ice is solid or frozen carbon dioxide that is frequently used as anexpendable refrigerant. Dry ice converts from a solid directly to a gasin the process known as sublimation. Water ice is another traditionalexpendable refrigerant, but has the disadvantage of converting to waterafter the ice melts. Dry ice is much denser and colder than traditionalice with a heat removal capability of approximately 254 btu/lb. Dry iceat atmospheric pressure is −109.3° F. (−78.5° C.) in comparison totraditional water ice 32° F. (0° C.). Dry ice sublimes by going directlyfrom a solid to a gas without passing through the liquid stage. The coldtemperature of dry ice and the fact that it leaves no residue like waterice makes it an excellent refrigerant for the transportation of chilledor frozen products. For example, the shipments that must remain frozenduring transportation can be packed with dry ice. The contents will befrozen when they reach their destination and there will be no messyliquid left over like traditional water ice.

Dry ice is generally stored in insulated containers prior to use toreduce the rate of sublimation. Losses due to ambient heat typicallyaverage 1-2%/day under ideal storage conditions. Based on storage orconditions of use the sublimation rate can be as high as 50%/day. Apound of dry ice after sublimation will convert to 8.5 cubic feet ofcarbon dioxide gas.

Unfortunately, while refrigeration can retard microbial growth, suchtreatment does not kill bacteria. Accordingly, microorganisms can stillsurvive through refrigeration, and worse, some microorganisms can stillgrow and produce harmful substances during refrigerated storage. Uponfumigation or other chemical treatment, another level of health problemsmay be created or the quality of the treated food may deteriorate. Forexample, chlorine has been widely used as a sanitizer of choice sinceWorld War I. However, concerns regarding the safety of carcinogenic andtoxic by-products of chlorine, such as chloramines and trihalomethanes,have been raised in recent years.

Ozone, an unstable, colorless gas with a distinct odor has been provento work more effectively on spoilage microorganisms than a classicdisinfectant such as chlorine. Due to its instability, the three oxygenmolecules of ozone break apart to form one diatomic oxygen molecule andanother free oxygen radical. This free oxygen radical attacks the cellwall and oxidizes it thus increasing the chance of permeability to theinner surfaces of the cell. This reaction of ozone on cell structures isirreversible; therefore the cells either become attenuated or die.Historically, ozone has been widely used for water treatment since theearly 1900's. Some well-known applications include disinfection ofswimming pools, spas, cooling towers, and sewage plants. Ozone isnormally produced by UV radiation with wavelengths below 200 nm or bythe corona discharge method that requires high electric energy.

Ozone has been used as a disinfectant/oxidant in the food industry forthe past several decades. It has been well applied to bulk storage (in a“room” type of storage facility) of produce (e.g. apples) or todisinfect water (e.g. municipal water or waste water treatment). Also,processes have been developed using ozone solutions (by injecting ozonegas through water) to sanitize/disinfect food products. Some examples ofusing ozone for sanitizing food products can be found in U.S. Pat. No.3,341,280 for sterilizing particulate food materials; U.S. Pat. No.4,849,237 which utilizes ozonated water for sanitizing poultrycarcasses; U.S. Pat. No. 5,011,699 which sterilizes food stuffs in aprocessing room with the aid of a mixture of ozone gas and carbondioxide gas and/or nitrogen gas; U.S. Pat. No. 5,405,631 directed tosanitizing citrus fruit with ultraviolet radiation and ozone generation;U.S. Pat. No. 6,210,730 directed to a method for treating perishablemeat products, including the steps of chilling the meat product,exposing the chilled meat product to a chilled gas mixture includingozone, and thereafter removing the chilled gas and exchanging that gaswith a mixture containing a high oxygen fraction; and U.S. Pat. No.6,458,398 which is directed to reducing the microbial population of foodin a container by the application of both a surfactant andozone-containing wash liquor to the food.

While ozone is highly water soluble and thus generally more effective inwater, it can be used effectively in the air as well, attacking yeastsand fungi as well as bacteria. In this regard, for nearly a century,ozone has been used as a food preservation agent for a wide variety ofperishable food items. Among the food items not mentioned previously andpotentially preserved by ozonation include potatoes, eggs, cheeses,bananas, berries, meats, carrots, onions, and peaches. Ozone dissolvedin water has also been used in food storage—including the preservationof fish in ozonated ice.

Carbon dioxide has natural properties that tend to inhibit the growth ofbacteria. These properties are use in controlled atmospheric packagingfor preserving food products. Carbon dioxide, however, is not aseffective nor as efficient as ozone at destroying bacteria. It would beuseful, therefore, to combine the cooling properties of solid dry icewith the pathogen destruction capability of ozone.

JP 071002240 describes a process to prepare a solid oxidizing agentcontaining ozone and chlorine to simultaneously provide the strongoxidizing property of ozone and continuous oxidizing capability ofchlorine to achieve an effective means for disinfection, sanitation,sterilization, prevention of food spoilage, deodorization, etc Severalmethods of preparation are provided:

-   -   1. Solid oxidizing agent formed by combining ices of        ozonated/chlorinated water and dry ice (CO₂) and solidified.    -   2. Solid oxidizing agent formed by combining ices of ozonated        water, ices of chlorinated water, and dry ice (CO₂).    -   3. Regarding the oxidizing agent described under 1. Oxidizing        agent characterized by its powdered form.    -   4. Regarding the oxidizing agent described under 1. Oxidizing        agent formed into various specific sizes and shapes.

JP 08107925 is similar to the above and is directed to a solid oxidizingagent comprising a mixture of ice of ozonated water and dry ice in apowdered form or other specific shape. The solid oxidizing agent isprepared by mixing powdered ice of ozonated water and powdered dry ice.The powdered mixture can then be custom made to a specific shape andsize. The composition can be used for disinfection, sanitation,sterilization, water purification, and odor removal. Prevention ofspoilage and odor of fresh foods is disclosed.

JP 3-217294 discloses a method of manufacturing ozonated water byabsorption of ozone in water containing carbon dioxide or carboniccompounds. The objective of the invention is to increase theconcentration of ozone into water in as much as high ozoneconcentrations in water cannot be achieved by conventional techniqueswhich simply dissolve ozone in the water. Accordingly, in this patent,carbon dioxide gas is flushed into water to produce CO₂-saturated water.An ozone gas mixture is then flushed into the CO₂-saturated water toform ozonated ice. Similarly, sodium bicarbonate-saturated water wasformed and then ozone was flushed into the carbonated water. Theinvention is stated as enabling the manufacturer of ozonated water andice at higher ozone concentrations than conventional manufacturingmethods. The ozone-containing composition in solid form can be used forsanitation purposes and for preserving fresh foods.

SU 1274645 by Rukavishni et al describes a method to prolong the storagelife and reduce produce losses of agricultural crops. As an example,rose petals are placed for storage at a low positive temperature, in ahermetically sealed polymeric container. Before loading the petals, thecontainer is treated with an air-ozone mixture with an ozone dose factorof 0.1 mg/l min. Dry ice is placed in the container, at a rate of 0.9 gper kg of stored produce. The rose petals are then loaded.

JP 09249510 discloses a method of controlling the emission of ozone fromsilica gel having adsorbed ozone. The silica gel having adsorbed ozoneis packed in a bag formed from a gas tight material and having a gascommunicating hole. The bag is wrapped with dry ice so that as the dryice sublimes, the temperature inside the bag increases and allows thedesorption of the ozone gas. The ozone gas is released from the bagthrough the hole.

SUMMARY OF THE INVENTION

This invention provides an effective means to improve a dry ice chillingprocess using ozone so that in combination, maximum biocidal efficacy isdelivered to ensure food safety and retain the wholesomeness of foodproducts.

Ozone is a very strong oxidizer and many food products are very delicatesubstrates. When food products are treated with ozone to remove anyharmful bacteria, the method of delivering the ozone to food productsand regulating it at the desired level are extremely important to ensurefood safety and maintain the wholesomeness of the food products. If theozone concentration is too high, oxidization and deterioration of thefood products that contact the ozone will cause significant economiclosses. If the ozone concentration is too low, the ozone alone may noteffectively kill unwanted bacteria.

Refrigeration using dry ice is one of the most effective processes thatretard the growth of unwanted bacteria and extend the shelf life of foodproducts. However, since refrigeration does not kill bacteria, and somebacteria or even pathogens can still grow slowly under refrigerationconditions, refrigeration alone poses certain serious problems to foodsafety.

This invention uses a multiple technologies approach, which hasadvantages over the use of a single technology. Combination of ozone anddry ice chilling results in much greater safety and quality of treatedfood products than would be expected using either technology alone.

In order to improve the quality and enhance the safety of food products,this invention provides an ozonated dry ice product. The combination ofozone and dry ice provides a means to kill bacteria while at the sametime provides for the chilling of a food product. Many bacteria have theability to repair themselves especially if they are given an opportunityto recover. Ozonated dry ice prevents bacteria from recovering andallows food processors to manufacture and transport a safer food productwith enhanced food quality.

The dry ice composition of this invention effectively delivers ozoneonto food products at a desired concentration through dry icesublimation. Ozone gas is slowly released as the dry ice sublimes andprovides a means to disinfect food products through direct food contactand ensure the significant reduction of spoilage and pathogenicmicroorganisms.

Any process capable of incorporating ozone into dry ice is useful toform the product of this invention. While not wishing to limit the dryice composition of this invention to any particular process of formingsame, the present invention also discloses several methods ofincorporating ozone into dry ice. The exemplified processes typicallyincorporate the ozone into the dry ice during the dry ice manufacturingprocesses. Dry ice manufacturing processes are known in the art and canbe readily manipulated to form the ozonated dry ice product of thisinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of a process of this invention for incorporatingozone into dry ice and forming pressed blocks of ozonated dry ice.

FIG. 2 is a schematic of a process of this invention for incorporatingozone into dry ice and forming extruded pellets of ozonated dry ice.

DETAILED DESCRIPTION OF THE INVENTION

In accordance with this invention there is provided an improved dry iceproduct manufactured in the form of blocks, pellets, flakes, powders,and other possible forms well known in the art containing carbon dioxideand ozone. The dry ice product is essentially free of water. What ismeant by “essentially free” of water is that the dry ice product, if itcontains water, will comprise less than 5 wt. % water. Typically, thewater content will be less than 1 wt. %. Moisture levels of up to 5,000ppm may be helpful in maintaining the desired shape of the product. Themajor constituent of the product is carbon dioxide. The ozoneconcentration in the product can vary widely and can depend upon the enduse of the product and, in particular, the product being treated and theenvironment surrounding the treated product. Only minute amounts ofozone are necessary for providing an antimicrobial effect. At the sametime, OSHA limits the exposure levels of ozone to 0.1 ppm to 0.3 ppm in8 hour and 15 minute shifts, respectively. Accordingly, the amounts ofozone dispersed into an area must be kept at a minimum and to a levelsafe for persons handling the treated product. A non-limiting level ofozone in the dry ice product can range from 0.1 ppm and above. Moretypically, the ozone content of the dry ice product will range fromabout 1 to 100 ppm. Ozone levels of 1 to 10 ppm by weight are believedto be effective for killing bacteria. Ozone present in the product ismade available for various applications during carbon dioxidesublimation with the additional benefits, i.e. chilling, of using dryice.

The product of this invention in which dry ice is combined with ozoneprovides an expendable form of refrigeration while simultaneouslyproviding a method of biological treatment that does not expose humanscoming in contact with the product to excessive levels of ozone. Ozonegas is generally considered to be an unstable molecule that has a shortshelf life. It is known that at lower temperatures ozone is more stableand has a reduced tendency to decompose to oxygen prior to providing anybiological effect. Dry ice at atmospheric pressure is at a temperatureof −109.9° F. The liquefaction temperature of ozone is −168° F. Thismeans that the ozone contained in the dry ice product is close to theliquefaction point, but still well into the gas phase. Accordingly, theozone mixed with dry ice as in the product of this invention can betrapped in the structural lattices of the dry ice and/or by physicalabsorption onto the surface of the dry ice. The ozone in the dry ice isadded for biological treatment. The most effective biocidal treatmentoccurs when the ozone is released in proportion with the dry icesublimation.

The exact form of the dry ice product can vary and, accordingly, a widevariety of forms can be manufactured and used depending upon the productto be treated and the purpose of such treatment such as, for example,storage, transport, commercial sale display, etc. Thus, if the productto be treated is to be stored in large rooms, for example, blocks of dryice ranging from 5 to 50 lbs. can be formed. Likewise, if the product tobe stored, transported, or displayed for sale requires direct contact ofthe dry ice product, smaller manufactured shapes can be provided. Thus,for example, pellets in the range of 1/16 to 1 inch can be formed, oreven powders such as snow, flakes, or chips can be formed by methodsknown in the art.

While the manufacturing process of the dry ice product can vary widelyand it is contemplated that any process which can incorporate ozone intodry ice can be found to yield a useful product, it has been found to beparticularly useful to incorporate the ozone into the carbon dioxideduring the dry ice manufacturing process.

The traditional first step in making “Dry Ice” is to manufacture carbondioxide liquid. This is done by compressing odor-free CO₂ gas andremoving any excess heat. Alternatively, odorous CO₂ gas may liquefiedand the liquid CO₂ rendered odor-free through the use of an adsorptivematerial such as activated carbon. The CO₂ is typically liquefied atpressures ranging from 200-300 pounds per square inch and at atemperature of −20° F. to 0° F. respectively. It is stored in a pressurevessel at lower than ambient temperature. The liquid pressure is thenreduced below the triple point pressure of 69.9 psig by sending itthrough an expansion valve. This can be done in a single step or, inmany cases, by reducing the liquid pressure to 100 psig at a temperatureof −50° F. as a first step to allow easy recovery of the flash gases.The liquid CO₂ is expanded inside a dry ice manufacturing press to forma mixture of dry ice solid and cold gas. The cold gas is vented orrecycled and the remaining dry ice snow is then compacted to formblocks. Dry ice is typically compacted to a density of approximately 90lb/ft3.

One of ordinary skill in the art will readily understand the presence ofodors in CO₂ may be determined by bubbling CO₂ gas through purifiedwater and smelling the headspace over the water or passing the gasthrough a cloth and then smelling the cloth. Such a one will recognizethat odor-free liquid CO₂ and odor-free solid CO₂ may also be subjectedto the foregoing tests by first subjecting such liquid or dry ice to acombination of temperature and pressure such that the CO₂ is present asa gas. Also, such a one will also readily understand that the presenceof odors in solid CO₂ may be determined by capturing a portion of thesolid on a cloth, allowing gaseous CO₂ to sublimate, and then smellingthe cloth. Methods of producing odor-free CO₂ are well known in the artand their details need not be duplicated herein. Typical of such methodsinclude a step of passing CO₂ gas through an adsorption unit containingactivated carbon or a catalytic oxidation unit employing a catalyst suchas platinum at a temperature of about 400° C.

The present invention facilitates the above by directly contactingcompressed ozone with carbon dioxide (which is odor-free). Incomparison, existing prior art as discussed previously dwells in usingindirect methods to combine ozone with dry ice after the dry ice ismanufactured. Such products include substantial amounts of water iceand, accordingly, inherit the problems associated with melting.

In general, to manufacture ozonated dry ice, compressed ozone at apressure of at least 90 psig is combined with odor-free liquid carbondioxide at a pressure above the triple point of CO₂ (70 psig), allowingthe ozone to fully dissolve in the liquid CO₂. The feed gas for ozoneinjection can include O₂, air, a mixture of O₂ and air or mixture of O₂,air, and an inert gas, e.g. N₂, CO₂, Ar, Kr, Xe, Ne.

Inert gas, if included with the ozone during contact with the CO₂, maycomprise 10-99% total concentration of injected gas in the process. Theinert gases may be mixed with ozone or added separately during theprocess. The temperature of the ozone treatment is maintained at ambientor below. CO₂ pressures ranging from 70 psig to 100 psig can be usedduring the mixing process. The ozone compression pressure will typicallyrange from about 100 to 150 psig. Higher ozone pressures can also beused when available. The liquid carbon dioxide/ozone mixture is thenexpanded to generate dry ice, “snow”, containing ozone, oxygen, and dryice—“ozonated dry ice.” This modified dry ice can then be collected orshaped such as by pressing or extrusion. This scheme can be successfullyadapted to existing dry ice plants.

Methods of producing ozone are well known in the art. Ozone is generatedusing oxygen or air. There are two primary methods of creating ozonefrom air: by an ultraviolet light generator light system or by anelectrical discharge system. An ultraviolet light ozone generatortypically consists of multiple ultraviolet light tubes within analuminum housing. In a multiple tube apparatus, air enters the generatorcavity and is subjected to the ultraviolet light and the ultravioletlight causes a disassociation of the oxygen molecules, which exists asO₂, to 2 oxygen atoms. Some of these oxygen atoms attach themselves tooxygen molecules to form ozone (O₃). The resulting ozone and sterile airmixture comprises approximately 0.2 percent of ozone by weight/weight ofair. In the preferred mode, the ozone gas is generated from oxygen oroxygen-enriched air by a corona discharge device that producesconcentrations ranging between about 1% to about 15% by weight of ozone.Based on technologies available today, it is possible to generate ozoneconcentrations up to a maximum of 13.5% with the remainder being oxygenand a small fraction of other gases. It is possible to use higher ozoneconcentrations for this application if the generator technology becomesavailable. Higher concentrations of ozone are preferred. It is preferredto use oxygen compared to air due to the possibility of producing higherconcentrations of ozone. It is industrially proven that ozone can becompressed to 150 psig using water ring compressors. It is feasible tosafely compress an ozone/oxygen mixture containing 10% by weight ofozone to 70 atm pressures. Several others have tried ozone liquefactionby using higher pressures without much success.

FIGS. 1 and 2 depict alternative methods of forming the ozonated dry iceproduct of this invention. Each figure represents a typical dry icemanufacturing process in which FIG. 1 is a process used to form blocksof dry ice, while FIG. 2 depicts a process used to form dry ice pellets.These processes can be modified to incorporate ozone into the dry iceproduct. First, with respect to FIG. 1, odor-free liquid carbon dioxideis stored in tank 2, typically at pressures of 200 to 300 psig. Theliquid carbon dioxide from storage tank 2 is then passed via line 4 to alow-pressure expansion tank 6 wherein the liquid CO₂ is expanded to apressure above the triple point of carbon dioxide (69.9 psig).Typically, the liquid CO₂ is expanded to pressures of from about 70 to100 psig in expansion tank 6. What results is a mixture of gas and adense, viscous carbon dioxide liquid. It is important that the liquidCO₂ is not formed into solid dry ice at this point in as much as thesolid in the piping would disadvantageously reduce transport of theliquid. Ozone from an ozone generator 8 is then injected into the liquidcarbon dioxide. Injection of the ozone can be done in the low-pressureexpansion tank although, as shown in FIG. 1, the ozone is mixed with theliquid CO₂ after the liquid CO₂ leaves expansion tank 6 via line 10.Ozone from the ozone generator 8 is compressed to pressures of fromabout 100 to 150 psig in compressor 12 and then fed via line 14 to mixwith the liquid CO₂ from line 10. The mixture of ozone and liquid CO₂ ispassed via line 16 through an expansion orifice 18 into the dry icepress 20. Alternatively, although not shown, the mixture of ozone andliquid CO₂ can be passed to a separate refrigeration unit, wherein theliquid CO₂ is frozen into a solid containing the entrapped ozone.

As further shown in FIG. 1, the mixture of liquid CO₂ and ozone isallowed to expand inside the dry ice press 20. During expansion, theliquid CO₂ is converted to a solid form and the ozone is trapped in thestructural lattices of dry ice and/or by physical absorption during dryice formation. The major portion of the ozone will remain attached tothe cold dry ice particles and only a small portion will exit dry icepress 20 with the flash gases via line 22. Once the dry ice solid isformed, the solid particles can be compressed via platen 24 in press 20into ozonated dry ice blocks 26.

The ozone in dry ice necessary for biological treatment is slowlyreleased as the carbon dioxide sublimes during use. Higherconcentrations and pressures of ozone are preferred to achieve higherconcentrations of ozone in the dry ice product. The preferredconcentration of ozone can vary depending upon the use of the dry iceand the product treated. By the above method it is possible to achievehigher concentrations of ozone compared to the prior art methods whichhave involved a mixture of ozonated water ice and dry ice. The presentmethod is relatively easy to implement in existing dry ice plants withminimum capital requirement.

Referring now to FIG. 2 which depicts a process used to form dry icepellets, such process is similar to that shown in FIG. 1. With respectto FIG. 2, odor-free liquid carbon dioxide is stored in tank 30, again,typically at pressures of 200 to 300 psig. The liquid carbon dioxidefrom storage tank 30 is then passed via line 32 directly to a dry icepelletizer 34. Dry ice pelletizers are well known in the art. It isbelieved any dry ice pelletizer is capable of use with this invention.In the pelletizer, the liquid CO₂ is expanded to a pressure below 70psig. What results is a mixture of gas and carbon dioxide solidparticles. Ozone from the ozone generator 34 is compressed to pressuresof at least about 100 psig in compressor 38 and then fed via line 40 tomix with the CO₂ in the dry ice pelletizer 34. Ozone injection can bedone prior to extrusion of the dry ice particles into pellets or theozone can be mixed with the CO₂ pellets after extrusion.

The liquid CO₂ is allowed to expand inside the dry ice pelletizer 34 andis converted to a solid form. While not wanting to be bound by anytheory of operation, if the ozone is added during expansion, the ozoneis believed to be trapped in the structural lattices of dry ice. If theCO₂ is solid, either as particles or as extruded pellets duringinjection of the ozone, the ozone is believed to be contained in the dryice by physical absorption. It is believed a major portion of the ozonewill remain attached to the cold dry ice particles and only a smallportion will exit with the flash gases from pelletizer 34 via line 42.The solid CO₂ particles are extruded into pellets, typically rangingfrom 1/16 to 1 in. As in the block dry ice, the ozone in dry ice pelletsnecessary for biological treatment is slowly released as the carbondioxide sublimes during use.

Small amounts of adjuvants may be added into the dry ice manufacturingprocess to improve the ozone stability in dry ice. Non-limiting usefuladjuvants are as follows:

-   -   a. Water (not to exceed 5 wt. % of dry ice)    -   b. GRAS (generally recognized as safe) grade acidulants such as        citric acid, acetic acid, lactic acid    -   c. GRAS grade surfactants such as polysorbate 60/65/80    -   d. GRAS grade food preservatives such as EDTA (in any forms),        BHA, BHT, sodium nitrate (in any forms).    -   e. GRAS gums such as carrageenan (in any forms), xanthan gum,        furcelleran (in any forms), arabinogalactan    -   f. Any other GRAS grade food additives such as polyethylene        glycol, sucrose fatty acid esters, fatty acids (in any forms)

The ozonated dry ice product of this invention improves the biocidalefficacy of dry ice to better ensure safe food production and maintainwholesomeness of the finished products. Ozone is effectively deliveredinto dry ice and at a desired concentration such that during dry icesublimation, the ozone can exert the desired biocidal effect fordisinfection and/or sanitation purposes. Ozone gas is released as aprocess to disinfect food products through direct food contact and toensure significant reductions of spoilage and pathogenic microorganisms.Since ozone is more stable under cold environments, the present processprovides the ultimate conditions for ozone to work at maximumreactivity. Since the release of ozone from the dry ice is wellregulated, food products receive ozone slowly and constantly during theentire storage thereof, and accordingly, shelf life and quality of thefood product are enhanced. Moreover, carbon dioxide chills the foodproducts efficiently, further providing benefits to food products. Thecarbon dioxide slows down the growth of spoilage and pathogenicmicroorganisms in food, allowing the food products to last longer andsafer. The carbon dioxide also slows down the enzymatic reactions infood, allowing the quality of food to be extended during storage. Carbondioxide from dry ice sublimation also penetrates into microbial cells,lowers the intracellular pH of microbial cells, and causes thosemicrobial cells to be more sensitive to ozone. Accordingly, asynergistic effect on biocidal efficacy can be achieved by combining dryice and ozone.

EXAMPLE

This example illustrates the injection of ozone into liquid CO₂. Avertical tubular reactor was provided made of SS 304 with a capacity ofabout 13 L. The top of this reactor included a lid containing inlet andexit ports for gaseous and liquid components. A liquid CO₂ supply vesselprovided a source of liquid CO₂.

The following operating procedure was utilized to form ozonated dry icesnow. A valve on the CO₂ supply vessel was opened and the reactor purgedwith gaseous CO₂ from the supply vessel. The reactor was allowed topurge for about 1-2 minutes. This was done in order to allow the vesselto be purged and minimize the chances of forming a short circuit. Afterabout 30 seconds, the reactor was again closed and the pressure adjustedto maintain 690 kPa (100 psig) in the reactor. The valve for directinggaseous CO₂ from the supply vessel was then closed.

The CO₂ liquid was then directed from the CO₂ supply vessel. Liquid CO₂was vented from the supply vessel until solid pieces of carbon dioxidebegan to appear in the vapor stream. Liquid CO₂ was then directed fromthe supply vessel to the reactor and the flow adjusted to increase ordecrease the flow of the liquid CO₂ into the reactor. The pressure inthe reactor was kept at 690-827 kPa (100-120 psig). It is important thatthe pressure does not go below the lower limit of this range. Thepressure can be reduced in the reactor if pressure exceeds 827 kPa (120psig). It is also useful to determine the liquid level in the reactorvia a dip tube. When the reactor was 66% to 75% full of liquid, liquidCO₂ flow to the reactor was stopped and the liquid CO₂ line from thesupply vessel was vented to ensure that no liquid was left in the line.The line was brought back to atmospheric pressure.

An insulated container was placed underneath the reactor to capturesnow. A small amount of snow was allowed to flow from the reactor bottomin order to make sure the opening was clear. The snow produced wasdiscarded. A backpressure regulator and reactor outlet was connected toan ozone destruction unit (glass vessel containing MnO₂). A gaseousozone line was connected to the inlet of the reactor. The pressure ofthe ozone system was maintained higher than the pressure of the reactor.The ozone gas line was purged and then the inlet ozone line to thereactor was slowly opened to adjust the flow rate of ozone into thereactor such that the flow of gas at the ozone destruction unit outletwas slow and steady. A slight pressure increase in the reactor isnormal, however, the pressure in the reactor was maintained such thatreactor pressure did not increase by more than about 34 kPa (5 psig).After the desired amount of ozone had been sent to the reactor or whenthe pressure of the ozone system approached the pressure of the reactor,the ozone inlet was closed.

The ozone-containing dry ice “snow” was directed from the bottom of thereactor into an insulated container until enough snow had been produced.

The ozone was produced from oxygen using an Ozonia® ozone generatorCFS-2 (Ozonia® Ltd., Switzerland). The ozone was collected and thencompressed to a maximum pressure of about 1034 kPa (150 psig).

Approximately one liter of CO₂/O₃ snow was collected and placed into abeaker. KI solution was added. The snow was allowed to completelysublime while the KI solution was constantly washed over the snow. Thesolution was titrated with 0.1N Na₂S₂O₃. This procedure followed theiodometric method of determining the amount of ozone present in thesample.

Results:

A first test run of the laboratory scale system described above producedabout 4 to 5 kg of ozonated snow. The amount of liquid carbon dioxide inthe reactor was about 9 L. Approximately 2 liters of compressed gas wastransferred into the liquid CO₂. The gas contained about 6.5% (wt/wt) O₃in O₂ with a gas pressure of about 814 kPa (118 psig). The snow that wasproduced during this test had an ozone concentration of about 2 ppm.

1. A manufactured dry ice product comprising ozone entrapped orphysically absorbed on or within odor-free solid carbon dioxide.
 2. Thedry ice product of claim 1 being essentially free of water.
 3. The dryice product of claim 2 optionally comprising less than 1 wt. % water. 4.The dry ice product of claim 1 optionally containing up to 5,000 ppmwater.
 5. The dry ice product of claim 1 in the form of shaped dry iceunits.
 6. The dry ice product of claim 5 wherein said dry ice units arecompression molded blocks.
 7. The dry ice product of claim 1 in the formof pellets.
 8. The dry ice product of claim 1 in the form of powder orflakes.
 9. The dry ice product of claim 1 wherein said ozone is presentin amounts of at least 0.1 ppm by weight.
 10. The dry ice product ofclaim 9 wherein said ozone is present in amounts of from 1 to 100 ppm.11. The dry ice product of claim 10 wherein said ozone is present inamounts of 1 to 10 ppm by weight.
 12. The dry ice of product claim 11being essentially free of water.
 13. The dry ice product of claim 12wherein said dry ice product optionally contains water in an amount ofless than 1 wt. %.
 14. A process for producing an ozonated dry iceproduct comprising contacting a gaseous ozone stream with odor-freeliquid carbon dioxide to form a mixture, subsequently cooling themixture of carbon dioxide and ozone to form dry ice solid containingozone entrapped or absorbed on or in said dry ice solid.
 15. The processof claim 14 wherein said liquid carbon dioxide is at a pressure of atleast 70 psig.
 16. The process of claim 15 wherein said gaseous ozone isat a pressure of at least 90 psig.
 17. The process of claim 14 whereinsaid gaseous ozone stream comprises a mixture of ozone and oxygen. 18.The process of claim 17 wherein said gaseous ozone stream optionallycontains an inert gas.
 19. The process of claim 14 wherein said dry icesolid is in the form of a powder or flake.
 20. The process of claim 14wherein said dry ice solid is compressed into blocks.
 21. The process ofclaim 14 wherein said dry ice solid is extruded into pellets.
 22. Theprocess of claim 14 wherein said liquid carbon dioxide is provided froma supply of liquid carbon dioxide at a pressure of from 200 to 300 psigand wherein said supply of liquid carbon dioxide is expanded to a lowerpressure of at least 70 psig.
 23. The process of claim 14 wherein saidmixture of ozone and liquid carbon dioxide is cooled by expansion in adry ice press, and said solid dry ice is pressed into blocks.
 24. Theprocess of claim 22 wherein said mixture of ozone and liquid carbondioxide is cooled by expansion in a dry ice press, and said solid dryice is pressed into blocks.
 25. The process of claim 22 wherein saidgaseous ozone stream is injected into said liquid carbon dioxide as saidsupply of liquid carbon dioxide is expanded to said lower pressure. 26.The process of claim 22 wherein said gaseous ozone stream is injectedinto said liquid carbon dioxide subsequent to said supply of liquidcarbon dioxide being expanded to said lower pressure.
 27. The process ofclaim 14 wherein said gaseous ozone stream comprises 10 to 15% by weightozone.
 28. A process of producing an ozonated dry ice product comprisingcontacting a gas stream containing ozone having a pressure of at least90 psig with odor-free dry ice so as to entrap or absorb said ozone. 29.The process of claim 28 wherein said dry ice is in the form of powder,flakes, or pellets.
 30. The process of claim 29 wherein said dry ice isin the form of powder or flakes and subsequent to contact with said gasstream, said powder or flakes are extruded into pellets.
 31. A method ofchilling a food product comprising placing a food product in theproximity of the manufactured dry ice product of claim 1 such thatduring sublimation of the dry ice, ozone is released therefrom forcontact with said food product, wherein said dry ice sol.
 32. Theprocess of claim 31 wherein said placed food product is in storageduring transport.
 33. The process of claim 31 wherein said placed foodproduct is in stationary storage.
 34. The process of claim 31 whereinsaid dry ice is in the form of blocks.
 35. The process of claim 31wherein said dry ice is in the form of powder, flakes, or pellets andsaid dry ice is placed in contact with said food product.
 36. Theprocess of claim 31 wherein said dry ice is essentially free of water.37. The process of claim 31 wherein said dry ice optionally containswater up to less than 1 wt. %.
 38. The process of claim 31 wherein saiddry ice optionally contains water up to 5,000 ppm by weight.
 39. Theprocess of claim 31 wherein said dry ice contains at least 0.1 ppm byweight ozone.
 40. The process of claim 31 wherein said dry ice contains1 to 100 ppm by weight ozone.
 41. The process of claim 31 wherein saiddry ice contains 1 to 10 ppm by weight ozone.
 42. The process of claim41 wherein said dry ice is essentially free of water.
 43. The process ofclaim 41 wherein said dry ice optionally contains water in amounts lessthan 1 wt. %.
 44. The process of claim 41 wherein said dry iceoptionally contains water in amounts of up to 5,000 ppm by weight.